Electrochemical treatment of landfill leachate for nitrogen removal

Abstract

Landfill has been employed as the most common method of solid waste disposal. Leachate collected from landfills is a special municipal waste liquid, and its treatment is both difficult and expensive. Landfill leachate usually has a NH4+-N concentration of more than 3000 mg/L together a large amount of refractory organic pollutants. Current leachate treatment methods, including air striping and biological reactions, are either too expensive or less effective in actual applications. The electrochemical (EC) process may be considered as a novel and effective method for leachate treatment. In the present study, a laBscale EC system was used for treatment of actual leachate collected from a landfill in Hong Kong. The raw leachate had a NH4+-N concentration of 3000-5000 mg/L and a chloride content of 2500-3500 mg/L. The EC system consisted of a DC power supplier, an EC reactor on a magnetic stirrer, and titanium-based mesh Ti/RuO2-ZrO2 electrode plates (5ï‚´4 cm2) immersed in the leachate. The electrodes had a gap of 5 mm between them, and a high current intensity was charged at 125 mA/cm2. The experimental results demonstrate that the EC process is highly effective for nitrogen removal from the landfill leachate. In batch tests, within 3 hrs of the EC treatment, complete denitrification could be achieved. Adding NaCl into the solution could further increase the rate of EC denitrification. The EC tests also were conducted using a CFSTR reactor with continuous leachate inflow and outflow. With a hydraulic retention time (HRT) of 5 hrs in the CFSTR, 3000 mg/L of NH4+-N could be removed completely. Electro-chlorination is believed to be the main mechanism of EC denitrificaiton. The EC process was also highly effective in decoloring of the leachate. In general, the EC method has the potential to be developed as a cost-effective alternative for treatment of landfill leachate.